# Patent

## Title
Controlled closing of MEMS switches

## Abstract

For the present invention, multiple MEMS switches that are similar in nature are provided along with switch control circuitry. Of the MEMS switches, one MEMS switch is reserved as a dummy MEMS switch while the one or more remaining MEMS switches are active, and are thus used during normal operation of the electronic circuitry that incorporates the MEMS switches. The switch control circuitry will use the dummy MEMS switch to adaptively determine an actuation signal that is sufficient to effect a near closing or soft closing of the dummy MEMS switch. The switch control circuitry may also determine a closing time that defines a time when the dummy MEMS switch closes relative to application of the actuation signal. The actuation signal and closing time may be updated regularly, if not continuously.

## Background
This application claims the benefit of U.S. provisional patent application Ser. No. 60/941,048 filed May 31, 2007, the disclosure of which is incorporated herein by reference in its entirety.


CROSS-REFERENCE TO RELATED APPLICATION
This application is related to U.S. patent application Ser. No. 12/118,031 entitled CONTROLLED OPENING OF MEMS SWITCHES, which is being filed concurrently, is incorporated herein by reference in its entirety, and forms part of the specification and teachings herein.
FIELD OF THE INVENTION
The present invention relates to micro-electro-mechanical system (MEMS) switches, and in particular to controlling actuation of MEMS switches to improve performance.
BACKGROUND OF THE INVENTION
As electronics evolve, there is an increased need for miniature switches that are provided on semiconductor substrates along with other semiconductor components to form various types of circuits. These miniature switches often act as relays, and are generally referred to as micro-electro-mechanical system (MEMS) switches. In many applications, MEMS switches may replace field effect transistors (FETs), and are configured as switches to reduce insertion losses due to added resistance as well as parasitic capacitance and inductance inherent in providing FET switches in a signal path. MEMS switches are currently being considered in many radio frequency (RF) applications, such as antenna switches, load switches, transmit/receive switches, tuning switches, and the like.
Turning to FIGS. 1A and 1B, a MEMS device 10 having a MEMS switch 12 is illustrated according to one embodiment of the present invention. The MEMS switch 12 is formed on an appropriate substrate 14. The MEMS switch 12 includes a movable member, such as a cantilever 16, which is formed from a conductive material, such as gold. The cantilever 16 has a first end and a second end. The first end is coupled to the substrate 14 by an anchor 18. The first end of the cantilever 16 is also electrically coupled to a first conductive pad 20 at or near the point where the cantilever 16 is anchored to the semiconductor substrate 14. Notably, the first conductive pad 20 may play a role in anchoring the first end of the cantilever 16 to the semiconductor substrate 14 as depicted.
The second end of the cantilever 16 forms or is provided with a cantilever contact 22, which is suspended over a contact portion 24 of a second conductive pad 26. Thus, when the MEMS switch 12 is actuated, the cantilever 16 moves the cantilever contact 22 into electrical contact with the contact portion 24 of the second conductive pad 26 to electrically connect the first conductive pad 20 to the second conductive pad 26. The MEMS switch 12 may be encapsulated by one or more encapsulating layers 30, which form a substantially hermetically sealed cavity about the cantilever 16. The cavity is generally filled with an inert gas and sealed in a near vacuum state. Once the encapsulation layers 30 are in place, an overmold material 32 may be provided over the encapsulation layers 30 as part of a high volume packaging process.
To actuate the MEMS switch 12, and in particular to cause the cantilever 16 to move the cantilever contact 22 into contact with the contact portion 24 of the second conductive pad 26, an actuator plate 28 is disposed over a portion of the substrate 14 and under the middle portion of the cantilever 16. To actuate the MEMS switch 12, an electrostatic voltage is applied to the actuator plate 28. The presence of the electrostatic voltage over time creates a field that moves the metallic cantilever 16 toward the actuator plate 28, thus moving the cantilever 16 from the position illustrated in FIG. 1A to the position illustrated in FIG. 1B.
Unfortunately, actuation of a MEMS switch 12, especially one maintained at near vacuum conditions, results in the cantilever 16 moving downward with a momentum sufficient to cause the cantilever contact 22 to bounce one or more times off of the contact portion 24 of the second conductive pad 26 after initial contact. Such bouncing degrades circuit performance and effectively increases the closing time. The article entitled “A Dynamic Model, Including Contact Bounce, of an Electrostatically Actuated Microswitch,” by Brian McCarthy et al., provides a detailed analysis of this bouncing phenomenon and is incorporated herein by reference. The dynamic closing forces may also be sufficient to damage both the contact portion 24 of the second conductive pad 26 as well as the cantilever contact 22, thus causing excessive wear, which results in a shortened operating life for the MEMS switch 12.
As a result, efforts have been made to control the force at which the cantilever 16 is pulled down to reduce bouncing. In particular, an actuation signal having a special waveform is initially applied to the actuator plate 28. The actuation signal moves the cantilever 16 downward, such that the contact pad 22 at the end of the cantilever 16 initially moves rapidly toward the contact portion 24 of the second conductive pad 26. The actuation signal is configured such that the effective electrostatic voltage is reduced or removed prior to the cantilever contact 22 coming into contact with the contact portion 24 of the second conductive pad 26. The downward momentum will continue to move the cantilever 16 downward, albeit at a decreasing rate, wherein the contact pad 22 lands softly and slowly on the contact portion 24 of the second conductive pad 26. Once the MEMS switch 12 is closed, a hold signal is applied to actuator plate 28 to hold the cantilever 16 in a closed position such that the contact pad 22 is held in contact with the contact portion 24 of the second conductive pad 26. The article “A Soft-Landing Waveform for Actuation of a Single-Pole Single-Throw Ohmic RF MEMS Switch,” by David A. Czaplewski et al., provides a technique for providing a pre-determined actuation signal to control the closing of a MEMS switch 12 and is incorporated herein by reference.
Providing an actuation signal to effect soft closings of the MEMS switches 12 theoretically reduces bouncing and increases the operating life of the device. In practice however, process variation in the switch manufacture will reduce or eliminate the efficiency of a single waveform to effect soft closing as described.
For example, if the gap between the cantilever 16 and the actuator plate 28 increases due to manufacturing variation, a nominal actuation signal may not be strong enough to move the cantilever 16 enough to provide a soft closing. As such, when the hold signal is subsequently applied, bouncing may occur if the cantilever contact 22 is not proximate the contact portion 24 of the second conductive pad 26. Conversely, if the gap between the cantilever 16 and the actuator plate 28 decreases due to manufacturing variation the nominal actuation signal may be too much, thus causing a hard closing, which may induce bouncing or damage. Further, humidity, temperature, aging, and wear may play a role in changing the mechanical characteristics, and thus operation, of MEMS switches 12. Accordingly, there is a need for a technique to reduce or eliminate bouncing in MEMS switches 12 over various process variations and operating conditions.
MEMS switches 12 also have issues associated with being released from a closed position, or opening. The cantilever 16 is effectively a metallic beam, which is deflected when the MEMS switch 12 is closed and suspended in a natural state when the MEMS switch 12 is open. Releasing the MEMS switch 16 entails turning off the hold signal, and thus releasing the deflected cantilever 16 from the closed position. Once released, the cantilever 16 springs upward and begins mechanically oscillating up and down. Such mechanical oscillation is referred to as ringing, and in a cavity in a near vacuum state this ringing may continue for an extended period of time. Further, the magnitude and time of ringing may vary over various operating conditions and process variations.
If the cantilever 16 is still ringing when the next actuation signal is applied, the nominal actuation signal may not provide a soft closing given the cantilever's position, upward momentum, downward momentum, or a combination thereof. And, during this ringing, the electrical isolation provided by the switch may be reduced, effectively prolonging the true opening time of the switch. Accordingly, there is a further need for a technique to reduce or eliminate ringing of MEMS switches 12 over various operating conditions and process variations.
SUMMARY OF THE INVENTION
For the present invention, multiple MEMS switches that are similar in nature are provided along with switch control circuitry. Of the MEMS switches, one MEMS switch is reserved as a dummy MEMS switch while the one or more remaining MEMS switches are active, and are thus used during normal operation of the electronic circuitry that incorporates the MEMS switches. The switch control circuitry will use the dummy MEMS switch to adaptively determine an actuation signal that is sufficient to effect a near closing or soft closing of the dummy MEMS switch. The switch control circuitry may also determine a closing time that defines a time when the dummy MEMS switch closes relative to application of the actuation signal. The actuation signal and closing time may be updated regularly, if not continuously.
To close any one the active MEMS switches, the switch control circuitry will apply the adaptive actuation signal, which was derived from analyzing the closing of the dummy MEMS switch, to the active MEMS switch. Application of the actuation signal should result in a soft closing, or at least a near closing, of the active MEMS switch. To maintain the active MEMS switch closed, a hold signal is applied at the closing time. Given the near closing or soft closing in response to the actuation signal and the timely application of the subsequent hold signal, bouncing of the movable member, such as the cantilever, in the active MEMS switch is minimized, if not completely eliminated.
In another embodiment of the present invention, the switch control circuitry may provide a release signal configured to reduce or minimize ringing, which is normally associated with opening a MEMS switch from a closed position. When the hold signal is released, a release signal is applied to the actuator plate to slow the rate at which the movable member actually moves back toward the normal resting position. The normal resting position generally corresponds to a non-actuated state. By slowing down the rate at which the cantilever returns to a normal resting position after closing, mechanical oscillations are controlled, and thus, ringing of the active MEMS switches is minimized or eliminated.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.



BRIEF DESCRIPTION OF THE DRAWING FIGURES
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention.
FIGS. 1A and 1B illustrate an exemplary micro-electro-mechanical system (MEMS) switch in a resting and closed position, respectively.
FIG. 2 is a block representation of a mobile terminal according to one embodiment of the present invention.
FIG. 3 is a flow diagram illustrating an adaptive process for identifying an appropriate actuation signal according to one embodiment of the present invention.
FIG. 4 provides timing diagrams illustrating the position of the free end of a MEMS switch's cantilever in response to an adaptive actuation signal and a subsequent hold signal according to one embodiment of the present invention.
FIG. 5 is a flow diagram illustrating a process for closing a MEMS switch using an adaptive actuation signal according to one embodiment of the present invention.
FIG. 6 illustrates mechanical oscillation, or ringing, of the free end of a MEMS switch's cantilever after releasing a hold signal according to one embodiment of the present invention.
FIG. 7 is a flow diagram illustrating a process for opening a MEMS switch using a release signal according to one embodiment of the present invention.
FIG. 8 provides timing diagrams illustrating the position of the free end of a MEMS switch's cantilever in response to successive application of an adaptive actuation signal, a hold signal, and a release signal according to a first embodiment of the present invention.
FIG. 9 provides timing diagrams illustrating the position of the free end of a MEMS switch's cantilever in response to successive application of an adaptive actuation signal, a hold signal, and a release signal according to a second embodiment of the present invention.
FIG. 10 provides timing diagrams illustrating the position of the free end of a MEMS switch's cantilever in response to successive application of an adaptive actuation signal, a hold signal, and a release signal according to a third embodiment of the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
The present invention may be incorporated in a mobile terminal, such as a mobile telephone, wireless personal digital assistant, or like communication device, in various ways. In many applications, MEMS switches 12 are being deployed as antenna switches, load switches, transmit/receive switches, tuning switches and the like. FIG. 2 illustrates an exemplary embodiment where numerous MEMS switches 12 are employed in a transmit/receive switch of a mobile terminal 34. Prior to delving into the details of the invention or the illustrated antenna switch, an overview of the basic architecture of the mobile terminal 34 is provided.
As illustrated, the mobile terminal 34 may include a receiver front end 36, a transmitter section 38, an antenna 40, and a transmit/receive switch 42, which includes four active MEMS switches 12R1, 12R2, 12T1, and 12T2, switch control circuitry 44 and a test MEMS switch 46. The mobile terminal 34 is capable of operating in two different bands while using a single antenna 40. As such, both the receiver front end 36 and the radio frequency transmitter section 38 are coupled to the antenna 40 through two different paths. Each path includes one of the active MEMS switches 12R1, 12R2, 12T1, and 12T2.
When receiving in the first band, the active MEMS switch 12R1 is closed, while the other active MEMS switches 12R2, 12T1, and 12T2 are open. When transmitting in the first band, the active MEMS switch 12T1 is closed, while the active MEMS switches 12R1, 12R2, and 12T2 are open. When receiving in the second mode, active MEMS switch 12R2 is closed, while the other active MEMS switches 12R1, 12T1, and 12T2 are open. Similarly, when transmitting in the second mode, active MEMS switch 12T2 is closed while the other active MEMS switches 12R1, 12R2, and 12T1 are open. Thus, signals received by or transmitted from the antenna 40 are selectively routed between the receiver front end 36 and the radio frequency transmitter section 38 based on the selected band. Control of the active MEMS switches 12R1, 12R2, 12T1, and 12T2 is provided by the switch control circuitry 44, which provides actuation signals to the actuator plates 28 (FIGS. 1A and 1B) to provide a soft closing of the active MEMS switch 12, and when the active MEMS switch is closed, provide a hold signal to the actuator plate 28 to effectively hold the active MEMS switch 12 in the closed position. The hold signal is removed from the actuator plate 28 of the active MEMS switch 12 that is closed to allow the active MEMS switch 12 to return to its normal resting (open) position.
Notably, the switch control circuitry 44 is also associated with a dummy MEMS switch 46. As will be described in greater detail below, the switch control circuitry 44 will use the dummy MEMS switch 46 to adaptively control the actuation signals provided to the active MEMS switches 12R1, 12R2, 12T1, and 12T2. In particular, the switch control circuitry 44 will determine a test actuator signal that is sufficient to nearly or softly close the dummy MEMS switch 46 to prevent or minimize bouncing, and then provide actuator signals to close the active MEMS switches 12R1, 12R2, 12T1, and 12T2 based on the test actuator signal. The switch control circuitry 44 will also determine when the dummy MEMS switch 46 closes relative to the application of the actuation signal. The timing of the hold signal presented to the active MEMS switches 12R1, 12R2, 12T1, and 12T2 is based on when the dummy MEMS switch 46 closes in response to the same actuation signal.
In addition to adaptively determining an appropriate actuation signal and when to apply a hold signal to the active MEMS switches 12R1, 12R2, 12T1, and 12T2, the switch control circuitry 44 may also provide a release signal, which is configured to reduce or minimize ringing, which is normally associated with a MEMS switch 12 opening from a closed position. When the hold signal is released, a release signal is applied to the actuator plate 28 to substantially suppress ringing of the active MEMS switches 12R1, 12R2, 12T1, and 12T2. Again, further detail relating to controlling bouncing and ringing is provided below after the remaining overview of the basic architecture of the mobile terminal 34.
Continuing with FIG. 2, the mobile terminal 34 further includes a baseband processor 48, a control system 50, a frequency synthesizer 52, and an interface 54. The control system 50 may include or cooperate with the switch control circuitry 44 to control the active MEMS switches 12R1, 12R2, 12T1, and 12T2 to facilitate receiving and transmitting via the different modes as well as help suppress bouncing and ringing of the active MEMS switches 12R1, 12R2, 12T1, and 12T2 during closing and opening, respectively.
The receiver front end 36 receives information bearing radio frequency signals of a given mode from one or more remote transmitters provided by a base station. Low noise amplifiers 56 amplify the signal. Filter circuits 58 minimize broadband interference in the received signal, while downconversion and digitization circuitry 60 downconverts the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. The receiver front end 36 typically uses one or more mixing frequencies generated by the frequency synthesizer 52. The baseband processor 48 processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor 48 is generally implemented in one or more digital signal processors (DSPs).
On the transmit side, the baseband processor 48 receives digitized data, which may represent voice, data, or control information, from the control system 50, which it encodes for transmission. The encoded data is output to the transmitter section 38, where it is used by modulation circuitry 62 to modulate a carrier signal that is at a desired transmit frequency for the given mode. Power amplifier circuitry 64 amplifies the modulated carrier signal to a level appropriate for transmission according to a power control signal, and delivers the amplified and modulated carrier signal to antenna 40 through the transmit/receive switch 42.
A user may interact with the mobile terminal 34 via the interface 54, which may include interface circuitry 66, which is generally associated with a microphone 68, a speaker 70, a keypad 72, and a display 74. The microphone 68 will typically convert audio input, such as the user's voice, into an electrical signal, which is then digitized and passed directly or indirectly to the baseband processor 48. Audio information encoded in the received signal is recovered by the baseband processor 48, and converted by the interface circuitry 54 into an analog signal suitable for driving the speaker 68. The keypad 72 and display 74 enable the user to interact with the mobile terminal 34, input numbers to be dialed, address book information, or the like, as well as monitor call progress information.
With reference to FIG. 3, a process is provided for adaptively determining an appropriate actuation signal to use when closing the active MEMS switches 12R1, 12R2, 12T1, and 12T2 based on the closing characteristics of the dummy MEMS switch 46. Preferably, the dummy MEMS switch 46 is fabricated on the same semiconductor substrate 14 (FIGS. 1A and 1B) using the same process as used when fabricating the active MEMS switches 12R1, 12R2, 12T1, 12T2, and thus, will tend to perform substantially similarly to the active MEMS switches 12R1, 12R2, 12T1, 12T2. The switch control circuitry 44 is able to present various actuation signals to the dummy MEMS switch 46, as well as present a test signal across the input and output terminals of the dummy MEMS switch 46. Thus, the switch control circuitry 44 can detect when the dummy MEMS switch 46 closes by detecting when the test signal is passed from the input terminal to the output terminal of the dummy MEMS switch 46. Although these examples relate to normally open MEMS switches, the concepts apply to normally closed MEMS switches, as well as other bi-state or multi-state MEMS switches.
Initially, the switch control circuitry 44 may receive an instruction to close the dummy MEMS switch 46 from the control system 50 (step 100). The switch control circuitry 44 will obtain initial actuation signal information, which defines the actuation signal to use for closing the dummy MEMS switch 46 (step 102). Next, the switch control circuitry 44 will apply a test signal at the input terminal of the dummy MEMS switch 46, and an actuation signal to the control terminal, or actuator plate 28, of the dummy MEMS switch 46 based on the actuation signal information (step 104). The switch control circuitry 44 will then determine if the dummy MEMS switch 46 actually closes in response to application of the actuation signal (step 106). If the dummy MEMS switch 46 closed (step 108), the switch control circuitry will determine when the dummy MEMS switch 46 closed relative to when the actuation signal was applied (step 110). The switch control circuitry 44 may simply determine the time when the test signal was received at the output terminal of the dummy MEMS switch 46 relative to the application of the actuation signal to the control input of the dummy MEMS switch 46. The actuation signal information is then adjusted to effectively reduce the closing energy imparted to the cantilever 16 in response to application of the actuation signal for the next iteration (step 112). An effort is made to modify the actuation signal to reduce the closing energy imparted to the cantilever 16 in response to application of the actuation signal on subsequent closings. As such, the process may be configured to continue to adjust the actuation signal information to effectively reduce the closing energy imparted to the cantilever 16 in response to application of the actuation signal until the cantilever 16 of the dummy MEMS switch 46 does not close in response to application of the actuation signal.
If the switch control circuitry 44 determines that the dummy MEMS switch 46 did not close in response to the actuation signal (step 108), the actuation signal information is adjusted to effectively increase the closing energy imparted to the cantilever 16 in response to application of the actuation signal (step 114). As such, through numerous iterations, the actuation signal information is modified in an iterative fashion, wherein on one iteration the dummy MEMS switch 46 may close in response to the actuation signal, and on the subsequent iteration the dummy MEMS switch 46 may not close in response to the actuation signal. In either case, this iterative process effectively converges the actuation signal to a configuration that imparts enough energy to cause a soft closing or near closing of the cantilever 16, such that the cantilever contact 22 either gently touches the contact portion 24 of the second conductive plate 26, or stops just shy of the contact portion 24 of the second conductive plate 26. As such, subsequent application of a hold signal would either hold the dummy MEMS switch 46 in a closed position, or would move the cantilever contact 22 a short distance into contact with the contact portion 24 of the second conductive pad 26, and then hold the dummy MEMS switch 46 in the closed position. Notably, the short distance traveled by the cantilever contact 22 in response to the hold signal will not cause bouncing or excessive wear to the dummy MEMS switch 46.
For an active MEMS switch 12R1, 12R2, 12T1, 12T2, it is important to apply the hold signal substantially when the cantilever contact 22 initially contacts the contact portion 24 of the second conductive pad 26, or at a point when the cantilever contact 22 is closest to the contact portion 24 in response to application of the actuation signal. Doing so minimizes the potential for bouncing, and minimizes wear on both the cantilever contact 22 and the contact portion 24 of the second conductive pad 26. As such, the switch control circuitry 44 may continuously update the actuation signal information (step 116) after adjusting the actuation signal to either reduce or increase the closing energy imparted to the cantilever 16 used to close the dummy MEMS switch 46. The switch control circuitry 44 may also update the hold signal timing information, if available, based on when the dummy MEMS switch 46 closed relative to application of the actuation signal to the dummy MEMS switch 46 (step 118). As noted, this process will repeat to allow the switch control circuitry 44 to adaptively converge on actuation signal information that will produce an actuation signal that provides a soft or near closing of the dummy MEMS switch 46, as well as determine when the dummy MEMS switch 46 closes in response to application of the actuation signal.
Based on the actuation signal information and the hold signal timing information derived from operating the dummy MEMS switch 46, the switch control circuitry 44 will operate to apply the actuation signal based on the actuation signal information and subsequently apply a hold signal based on the hold signal timing information to a selected one or ones of the active MEMS switches 12R1, 12R2, 12T1, 12T2 during normal operation of the mobile terminal 34. Since the dummy MEMS switch 46 should have the same operating characteristics as the active MEMS switches 12R1, 12R2, 12T1, 12T2 due to their common fabrication characteristics and environment, the actuation signal and timing for applying the hold signal can be applied to the active MEMS switches 12R1, 12R2, 12T1, 12T2 to minimize bouncing and wear.
The iterative process provided in FIG. 3 may be implemented in various ways. For example, the process may be employed such that multiple iterations are employed to arrive at desired actuation signal information and hold signal timing information prior to operating any of the active MEMS switches 12R1, 12R2, 12T1, 12T2. Thus, initial operation of the active MEMS switches 12R1, 12R2, 12T1, 12T2 will use relatively optimized actuation signals, and the subsequent hold signals will be applied at a relatively optimized time in light of the hold signal timing information. In operation, every time a mode is selected or the mobile terminal 34 is powered on, the iterative process to obtain an optimal actuation signal and time for applying a hold signal is generated prior to initiating communications.
Alternatively, the switch control circuitry 44 may run the process in real time during operation of the mobile terminal 34, wherein the switch control circuitry 44 effectively applies an actuation signal based on the current actuation signal information to close the dummy MEMS switch 46 as well as any selected active MEMS switches 12R1, 12R2, 12T1, 12T2. In other words, the dummy MEMS switch 46 is closed when one of the active MEMS switches 12R1, 12R2, 12T1, 12T2 is closed. The switch control circuitry 44 will constantly adapt to existing conditions to ensure that the dummy MEMS switch 46 is coming to a near or soft close, adjust the actuation signal information as necessary, and provide an actuation signal based on the updated actuation signal information the next time an active MEMS switch 12R1, 12R2, 12T1, 12T2 (and perhaps the dummy MEMS switch 46) is closed. Additionally, the hold signal timing information is updated along with updating the actuation signal information such that the hold signal applied to the active MEMS switches 12R1, 12R2, 12T1, 12T2 tracks the updates for the actuation signal.
Notably, the actuation signal information and the hold signal timing information may be updated with every closing of any of the active MEMS switches 12R1, 12R2, 12T1, 12T2, or may be updated on a periodic basis after a certain number of closings or after a certain amount of time has passed. Thus, the process outlined in FIG. 3 may cycle through a given iteration every so many closings or after a certain amount of time. In such an embodiment, if the actuation signal information is far from optimal, the first few iterations of the process may result in significant bouncing. However, after a few iterations, a more optimal actuation signal and hold signal timing will be determined.
Turning to FIG. 4, timing diagrams are provided to illustrate the displacement of the cantilever 16 in light of application of an actuation signal and a subsequent hold signal according to one embodiment of the present invention. Notably, the cantilever displacement corresponds directly to the relative position of the cantilever contact 22 over the contact portion 24 of the second conductive pad 26. FIG. 4 is best described in association with the flow diagram of FIG. 5, which outlines the process for closing an active MEMS switch 12R1, 12R2, 12T1, 12T2. Initially, the active MEMS switch 12R1, 12R2, 12T1, 12T2 is open, and thus the cantilever 16 is in an open position. The switch control circuitry 44 will receive an instruction to close the active MEMS switch 12R1, 12R2, 12T1, 12T2 (step 200), and will apply an actuation signal to the active MEMS switch 12R1, 12R2, 12T1, 12T2 based on the actuation signal information, which was derived from the dummy MEMS switch 46 (step 202). The actuation signal illustrated in FIG. 4 includes a fixed voltage pulse for a time T1 followed by a rest period for time T2, wherein no voltage is applied to the control terminal or actuator plate 28. As illustrated, during time T1 where the pulse is being applied to the control terminal, the cantilever 16 begins to move downward at an increasingly rapid rate. When the voltage is removed from the control terminal during time T2, the downward movement of the cantilever 16 decreases and comes to a stop at a point where the cantilever contact 22 is just above the contact portion 24 of the second conductive pad 26, or the cantilever contact 22 comes into contact with the contact portion 24 of the second conductive pad 26 at the end of time T2. At the end of the actuation signal, the hold signal is applied for a time T3 (step 204). Application of the hold signal is based on the hold signal timing derived from the dummy MEMS switch 46.
Unfortunately, the closing of a MEMS switch 12 is not the only problematic aspect of operating the MEMS switch 12. As indicated above, opening the MEMS switch 12, and in particular releasing the cantilever 16 from a closed position by removing the hold signal, causes the free end of the cantilever 16 to mechanically oscillate, or ring. This ringing often lasts for an extended period of time, which may be longer than the time between closings. Thus, an actuation signal that is appropriate to close the MEMS switch 12 when the cantilever 16 is at rest will likely not be sufficient to provide a near or soft closing of the MEMS switch 12 when the cantilever 16 is still oscillating from a recent opening.
With reference to FIG. 6, the mechanical displacement of the free end of the cantilever 16 is illustrated after releasing a hold signal to allow a closed MEMS switch 12 to return to a normal resting position, which is an open position in the illustrated embodiments. As illustrated, the free end of the cantilever 16 begins in a closed position, and oscillates well above the normal resting (open) position of the cantilever 16. These oscillations continue such that the free end of the cantilever 16 oscillates above and below the normal resting (open) position. During operation, the position and movement associated with the cantilever 16 during these oscillations drastically change the response of the MEMS switch 12 to an otherwise appropriate actuation signal. Accordingly, another aspect of the present invention provides a release signal after the hold signal is removed in order to dampen the ringing normally associated with releasing a MEMS switch 12 from a closed position.
Returning to the exemplary embodiment illustrated in FIG. 2 along with reference to FIG. 7, a technique is presented to significantly reduce or eliminate ringing after a hold signal has been removed from one of the active MEMS switches 12R1, 12R2, 12T1, 12T2. Initially, the switch control circuitry 44 will receive an instruction to release one of the active MEMS switches 12R1, 12R2, 12T1, 12T2 from a closed position (step 300). The switch control circuitry 44 will then remove the hold signal from the active MEMS switch 12R1, 12R2, 12T1, 12T2 (step 302) and then apply a release signal to the active MEMS switch 12R1, 12R2, 12T1, 12T2 (step 304). The release signal is applied to the control input of the active MEMS switch 12R1, 12R2, 12T1, 12T2 and is configured to apply significant down force to the cantilever 16 to reduce the speed at which the cantilever 16 springs back toward the resting position. The release signal will not pull the cantilever 16 downward, but will instead simply slow the rate at which the cantilever 16 moves upward, such that the free end of the cantilever 16 does not significantly overshoot its normal resting position, and thus, significantly reduces or eliminates any mechanical oscillation of the free end of the cantilever 16. Thus, ringing is at worst reduced to a point where subsequent switch closings occur after any ringing is abated or reduced to a point of insignificance.
Like the actuation signal, the release signal may take various forms and may have portions wherein a voltage (or current) may be applied during release time, and no voltage (or current) may be applied at another portion of the opening time. With reference to FIG. 8, an exemplary release signal is illustrated along with the corresponding cantilever displacement. The application of the actuation signal and the subsequent hold signal is the same as that described in association with FIG. 4. When the hold signal is removed at the end of time T3 and the beginning of time T4, the release signal is applied. In this example, there is no voltage (or current) applied during time T4; however, at the end of time T4 and beginning of time T5, a pulse is applied for the remaining portion of the release signal. As such, the free end of the cantilever 16 will begin rising quickly when the hold signal is removed and throughout time T4. During time T5, the voltage is applied at the control input of the active MEMS switch 12R1, 12R2, 12T1, 12T2, and thus a down force is applied against the rising cantilever 16. The effect of the down force is sufficient to allow the cantilever 16 to decelerate as it approaches its normal resting position, thus minimizing ringing.
In this example, the release signal is effectively a mirror image of the actuation signal. Applicants' research has found that, in the case of a near vacuum environment for the cantilever, applying a mirror image of an appropriate actuation signal as a release signal is sufficient to significantly decrease, if not eliminate, oscillations after removing a hold signal.
With reference to FIGS. 9 and 10, various actuation signal profiles and corresponding release signals, which are effectively and substantially mirror images of the actuation signals, are illustrated. Those skilled in the art will recognize that the release signal does not have to be a mirror image of the actuation signal that is applied to close a MEMS switch 12; however, in one embodiment of the present invention, using a mirror image of the actuation signal as a release signal is an effective way of arriving at an appropriate release signal. Further, it is much easier to determine and select an actuation signal that provides a near or soft closing, because one can monitor when the MEMS switch 12 actually closes. When releasing a hold signal to open a MEMS switch 12, it is difficult to determine when ringing has substantially abated. Thus, basing the release signal on the actuation signal allows the release signal to be adapted to various environmental and process variations when used in conjunction with the adaptive actuation signal generation of one embodiment of the present invention.
With particular reference to FIG. 9, the actuation signal provides a fixed voltage (or current) during a time T1, and during time T2 a decaying voltage is applied until or slightly before a hold signal is applied at the end of time T2 and beginning of time T3. Correspondingly, the release signal begins during time T4 with an increasing voltage (or current) until the beginning of time T5, wherein a fixed voltage (or current) is applied throughout time T5. Notably, the magnitudes of the actuation signal, release signal, and hold signal may vary, if desired, in embodiments where analog signals are available. In digital control embodiments, the voltages (currents) applied throughout the actuation signal, hold signal, and release signal are preferably at the same level.
With reference to FIG. 10, a series of pulses such as those that may be provided during pulse width modulation (PWM) may make up the actuation signal or release signal. In FIG. 10, the actuation signal includes a series of three pulses provided during a time T1, wherein each pulse is followed by a period of no voltage (or current), and each successive pulse has a decreasing duration. Correspondingly, the release signal includes a series of pulses with increasing durations, which are spaced apart during time T3.
Those skilled in the art will recognize various ways in which to configure actuation and release signals in light of the teachings herein. These variations are considered within the scope of this disclosure and the claims that follow. Further, the adaptive process for determining actuation signals does not need to be combined with the use of release signals to minimize ringing. Similarly, a release signal may be used in an embodiment where the actuation signal is fixed, and not adapted in light of environmental and process variations.
Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

## Claims

1. A method for adaptively providing an actuation signal to apply when closing MEMS switches within a plurality of MEMS switches within a single transmit/receive switch, the method comprising:
iteratively determining an actuation signal required to cause a soft closing of a first MEMS switch of the plurality of MEMS switches that resides within the single transmit/receive switch; and
effecting closing of a second MEMS switch that resides in plurality of MEMS switches that reside within the single transmit/receive switch by applying the actuation signal to the second MEMS switch and subsequently applying a hold signal to the second MEMS switch to maintain the second MEMS switch in a closed position, wherein the actuation signal used to close the second MEMS switch is repeatedly updated based on operation of the first MEMS switch,
wherein the first MEMs switch is a dummy MEMS switch that is dedicated for determining the actuation signal in light of current conditions.

2. The method of claim 1 further comprising, in association with iteratively determining the actuation signal, determining a closing time identifying a time at which the soft closing occurs in the first MEMS switch relative to application of the actuation signal, wherein effecting closing of the second MEMS switch is afforded by applying the actuation signal to the second MEMS switch and subsequently applying the hold signal to the second MEMS switch at the closing time to maintain the second MEMS switch in a closed position.

3. The method of claim 1 wherein iteratively determining the actuation signal to cause the soft closing of the first switch further comprises iteratively:
applying the actuation signal to a control terminal of the first MEMS switch;
determining whether the first MEMS switch closes in response to application of the actuation signal;
adjusting the actuation signal to impart greater closing energy, if the first MEMS switch does not close in response to the actuation signal; and
adjusting the actuation signal to provide less closing energy, if the first MEMS switch closes in response to application of the actuation signal.

4. The method of claim 3 wherein the determining whether the first MEMS switch closes in response to application of the actuation signal comprises:
applying a test signal at an input of the first MEMS switch in association with applying the actuation signal to the control terminal of the first MEMS switch; and
detecting the test signal at an output of the first MEMS switch to determine that the first MEMS switch closed in response to application of the actuation signal.

5. The method of claim 4 further comprising, in association with iteratively determining the actuation signal, determining a closing time identifying a time at which the soft closing occurs in the first MEMS switch relative to application of the actuation signal by detecting when the test signal is detected at the output of the first MEMS switch when the first MEMS switch closes in response to application of the actuation signal, wherein effecting closing of the second MEMS switch is afforded by applying the actuation signal to the second MEMS switch and subsequently applying the hold signal to the second MEMS switch at the closing time to maintain the second MEMS switch in a closed position.

6. The method of claim 3 wherein each time the actuation signal is adjusted in relation to the first MEMS switch, actuation signal information defining the actuation signal is updated and the actuation signal information is used to subsequently generate the actuation signal for closing the second MEMS switch.

7. The method of claim 6 wherein the actuation signal information is also used to generate the actuation signal for closing the first MEMS switch.

8. The method of claim 1 wherein the actuation signal comprises a first signal period having a first voltage or current waveform followed by a second signal period having a second voltage or current waveform that is different from the first voltage or current waveform.

9. The method of claim 1 wherein the actuation signal comprises a first signal period having a voltage or current waveform followed by a second no signal period having no voltage or current waveform.

10. The method of claim 9 wherein a pulse waveform is provided during the first signal period.

11. The method of claim 1 wherein the actuation signal comprises a decaying voltage or current waveform.

12. The method of claim 1 wherein the actuation signal is a pulse width modulation signal.

13. The method of claim 1 wherein the actuation signal comprises a series of pulses separated by periods having no voltage or current waveforms.

14. The method of claim 1 wherein the second MEMS switch is part of active circuitry in the single transmit/receive switch.

15. The method of claim 14 further comprising effecting closing of a third MEMS switch that resides in the single transmit/receive switch-electronic circuit by applying the actuation signal to the third MEMS switch and subsequently applying the hold signal to the third MEMS switch to maintain the third MEMS switch in a closed position.

16. The method of claim 15 wherein the second MEMS switch is closed at a different time than the third MEMS switch.

17. A system for adaptively providing an actuation signal to apply when closing MEMS switches in a plurality of MEMS switches within a single transmit/receive switch comprising:
a first MEMS switch;
a second MEMS switch, both first and second MEMS switches within the single transmit/receive switch; and
switch control circuitry adapted to:
iteratively determine an actuation signal required to cause a soft closing of the first MEMS switch that resides in the single transmit/receive switch; and
effect closing of the second MEMS switch that resides in the transmit/receive switch by applying the actuation signal to the second MEMS switch and subsequently applying a hold signal to the second MEMS switch to maintain the second MEMS switch in a closed position, wherein the actuation signal used to close the second MEMS switch is repeatedly updated based on operation of the first MEMS switch, wherein the first MEMS switch is a dummy switch that is dedicated for determining the actuation signal in light of current conditions.

18. The system of claim 17 wherein in association with iteratively determining the actuation signal, the switch control circuitry is further adapted to determine a closing time identifying a time at which the soft closing occurs in the first MEMS switch relative to application of the actuation signal, wherein effecting closing of the second MEMS switch is afforded by applying the actuation signal to the second MEMS switch and subsequently applying the hold signal to the second MEMS switch at the closing time to maintain the second MEMS switch in a closed position.

19. The system of claim 17 wherein to iteratively determine the actuation signal to cause the soft closing of the first switch, the switch control circuitry is further adapted to:
apply the actuation signal to a control terminal of the first MEMS switch;
determine whether the first MEMS switch closes in response to application of the actuation signal;
adjust the actuation signal to impart greater closing energy, if the first MEMS switch does not close in response to the actuation signal; and
adjust the actuation signal to provide less closing energy, if the first MEMS switch closes in response to application of the actuation signal.

20. The system of claim 19 wherein to determine whether the first MEMS switch closes in response to application of the actuation signal, the switch control circuitry is further adapted to:
apply a test signal at an input of the first MEMS switch in association with applying the actuation signal to the control terminal of the first MEMS switch; and
detect the test signal at an output of the first MEMS switch to determine that the first MEMS switch closed in response to application of the actuation signal.

21. The system of claim 20 wherein in association with iteratively determining the actuation signal, the switch control circuitry is further adapted to determine a closing time identifying a time at which the closing occurs in the first MEMS switch relative to application of the actuation signal by detecting when the test signal is detected at the output of the first MEMS switch when the first MEMS switch closes in response to application of the actuation signal, wherein effecting closing of the second MEMS switch is afforded by applying the actuation signal to the second MEMS switch and subsequently applying the hold signal to the second MEMS switch at the closing time to maintain the second MEMS switch in a closed position.

22. The system of claim 19 wherein each time the actuation signal is adjusted in relation to the first MEMS switch, actuation signal information defining the actuation signal is updated, and the actuation signal information is used to subsequently generate the actuation signal for closing the second MEMS switch.

23. The system of claim 22 wherein the actuation signal information is also used to generate the actuation signal for closing the first MEMS switch.

24. The system of claim 17 wherein the actuation signal comprises a first signal period having a first voltage or current waveform followed by a second period having a second voltage or current waveform that is different from the first voltage or current waveform.

25. The system of claim 17 wherein the actuation signal comprises a first signal period having a voltage or current waveform followed by a second no signal period having no voltage or current waveform.

26. The system of claim 25 wherein a pulse waveform is provided during the first signal period.

27. The system of claim 17 wherein the actuation signal comprises a decaying voltage or current waveform.

28. The system of claim 17 wherein the actuation signal is a pulse width modulation signal.

29. The system of claim 17 wherein the actuation signal comprises a series of pulses separated by periods having no voltage or current waveforms.

30. The system of claim 17 wherein the second MEMS switch is part of active circuitry in the single transmit/receive switch.